[css-inline] vertically align to middle of cap height

vertical-align: middle will align an element with the baseline of text minus half its x-height. This makes it a poor fit for glyph-sized elements like icons, which will always look a tad too low. Ideally we’d have a keyword (vertical-align: text-middle?) that would align with the middle of the cap height of the typeface instead…

In lieu of this property, I see two dominant techniques for accomplishing this:

• The icon position is adjusted manually, using top: -1px or similar. This requires the icon to be inline-block, since other positioning techniques will conflict with the top value.
• The icon and text must be wrapped in a container with display: flex; align-items: center or similar. But this prevents the icon from being used inline.

(I was encouraged to submit this issue after writing about the idea.)

Start with the issue description of vertical-align: middle, the proposed text-middle keyword, and the linked typeface-median article. Compare the two existing alignment techniques described there and determine the specification and design work needed for cap-height alignment; done means the CSS Working Group has a settled, implementable direction.